The present invention is generally concerned with light fittings comprising a base adapted to be mounted on a support of any kind, for example, and a diffuser mobile relative to the base and able to move between two positions, namely a closed position in which it prevents access to the interior volume of the unit and an open position in which it enables such access. A closure device operative between the diffuser and the base releasably locks the diffuser to the base. A safety switch controlling the electrical power supply to the unit is open when the diffuser is in its open position.
The present invention is more particularly directed to the situation in which the closure device includes a slider operated by actuator means accessible to the user from the outside and moving longitudinally on the base between a closed position and an open position respectively corresponding to the closed position and the open position of the diffuser. Coupling means operative at least locally on the path of movement of the slider enable the diffuser to be hooked onto the slider.
Such light fittings are used in explosive atmospheres, for example.
When a light fitting of this kind is opened, for example to carry out a maintenance operation, its power supply is normally systematically isolated as soon as it opens and is normally not reconnected until it has been closed.
Thus the operative can normally work in complete safety and there is normally no risk of any sparks occurring while the operative is working.
In practice, however, the means provided for this purpose can be faulty.
The safety switch may be inadvertently closed when the diffuser is in the open position, for example.
Or the safety switch may be stuck in the closed position when the diffuser is opened.
Such incidents can obviously have serious consequences.
A general object of the present invention is a totally safe way to prevent such incidents.
To be more precise, the present invention consists in a light fitting of the above kind which is generally characterized in that the slider is associated with releasable immobilizing means operated by the diffuser and adapted to oppose movement of the slider in the direction toward its closed position when the diffuser is in its open position and in that the safety switch is itself operated by the slider.
This prevents unintentional movement of the slider when the diffuser is in the open position and the slider is therefore prevented from operating the safety switch when the diffuser is in the open position.
In one preferred embodiment of the invention, the slider carries a ramp which positively opens the safety switch when it is in its open position.
In other words, in this embodiment of the invention, the slider holds the safety switch open when it is in its open position.
In other words, and in contrast to the usual arrangements, the safety switch is operated when the diffuser is open instead of unoperated.
This advantageously prevents all risk of the safety switch being stuck in the closed position when the diffuser is opened, which is to the benefit of safety.
Likewise, the slider covers the safety switch when the diffuser is in the open position and therefore prevents operation of the switch, which prevents all risk of unintentional operation of the safety switch when the diffuser is in the open position, which is again beneficial to safety.
In another preferred embodiment of the invention, when the slider operating means include a pinion rotating on the base and meshing with a rack fastened to the slider, which is the usual arrangement, the height of the teeth of the rack progressively decreases at one end at least of the rack.
The pinion can therefore escape from the rack at the end of its travel, which has the advantage of limiting the loads applied to the system and that the resulting rasping noise tells the operator that the rack has reached the end of its travel if the operator has failed to notice this by any other means.